The orifice plate of a print head in an ink jet primer tends to collect debris such as paper dust during the printing process. The debris adheres to the orifice plate due to the occasional accumulation of ink droplets or an electrostatic charge. If left dirty, the accretion of debris and ink may impair printing quality by blocking or deflecting the passage of ink droplets during priming.
Some existing printers remove such debris with wipers that function as squeegees. A typical wiper has a cantilevered elastomeric blade extending perpendicularly to the orifice plate. As the plate slides past the blade, the blade is deflected to contact the plate at an "angle of attack" that varies with the spacing between the wiper and the plate. Variations in the angle of attack result in an undesirable variation in wiping effectiveness. For instance, reduced spacing causes the blade to bend excessively to a zero angle of attack in which a face of the blade presses against the plate and the desired scraping effect of the blade edge is lost. While an oblique angle of attack is desired, the normal force of the wiper varies too greatly with small spacing variations, necessitating a lesser contact angle to maintain normal forces within acceptable ranges as the spacing varies within tolerances. In addition, even with a tolerable range of variation of the normal force, a cantilevered wiper is prone to non linearity of response. That is, it has a spring constant that varies over the range of motion; beyond a certain displacement, no more force may be generated.
Existing cantilevered blade wipers rely on the softness of the material to provide flexing and a spring force. The geometry of a cantilever requires that a relatively soft material be used to provide adequate flexing. This forces the use of materials that wear more readily at the contact edge, and which are less effective at dislodging tenacious debris. Also, such existing wipers are not useful for bidirectional wiping, because the blade is susceptible to buckling in the opposite direction.
These disadvantages are overcome by providing a wiper having a flexible, elongated body that is supported by a rigid frame at spaced-apart support points on the body. A wiper nib is connected to the body at an intermediate point between the support points. The nib and body may be integrally formed as a single elastomeric member, and the body may be curved to form an elongated arc to generate compressive strain in the body in response to deflection of the tip in a lateral direction.